Con rod query

[Steve Jones]

Shells or white metal? I discussed this last night with my mentor Nick Turley. Nick made the point that white metal is much more forgiving than shells when it comes to the crud that inevitably circulates in a traditional splash fed set up. As I do not want to get into fitting an oil filter I have decided to stick with white metal.

Which is as we discussed on the phone on Sunday, Colin. 

It's the right way to go and you're booked in for the metalling at the right place. 

There again, Nick and I rarely disagree on such matters!!  

Steve

[Hugh Barnes]

Not in my experience Charles, having campaigned my Pearl with a 3 bearing engine for the last 15 years or more (including 2 Eurotours).

It was tongue in cheek Hugh!

Ah, well, that would explain it! However, picking up on Jon’s comment, it is worth saying that the bottom end of this engine was line bored and set up for me by Vince Leek, which probably accounts for its longevity. But even then, a few years back, I did have to slip new centre bearing shells in place as the infamous ‘centre bearing knock’ had joined all the other noises the car makes..

[Chris KC]

Unless finished in place all shells are made with an exaggerated clearance at the parting line although it may not be obvious.

Bob, surely you mean interference? (or 'crush' as it's known in the trade). The shells stand a few thou proud of their housing so they are forced firmly into it on assembly. It is this radial force (not the tabs) which prevents the bearing shells turning in service. I have read write-ups ascribing this to 'wear' of the housing and advocating shimming it out, I submit that's not a great idea.

[Zetomagneto]

Shells or white metal? I discussed this last night with my mentor Nick Turley. Nick made the point that white metal is much more forgiving than shells when it comes to the crud that inevitably circulates in a traditional splash fed set up. As I do not want to get into fitting an oil filter I have decided to stick with white metal.

Hi Colin, if I understand correctly you are using a new crank with remetaled Nippy rods?
Bear in mind you will need to get the rods narrowed to fit the crank, you will have no white metal
on the sides of the bearing housing although that is not a problem as new rods run steel to steel with no problem.You will also have to find some suitable bigend bolts from somewhere as the Nippy ones are quite different to ordinary ones.

Hi Jon, I would not use shell bearings without a flter, shells will not tolerate foreign matter.
I have Saenz conrods, shell bearings, and a full flow filter on my heavy 12/4.

My Phoenix cranked Seven Engine has a filter, they are not difficult to fit, and apart from tapping deeper into the jet gallery to fit the bung, no real modification,and can revert to original if wanted.

Hi Terry, my question of why holes in the rods has not been answered, for me drilling holes into the bearing housing will result in no hydrodynamic oil pressure.
If the holes are drilled for increased oil flow, surely this can be achieved by increasing the side clearance.
Best Wishes & happy Sevening to all

[Terrytuned]

Zeto you can increase side clearance to improve flow but you need to get some heat into the oil before driving,you get a better flow through by drilling.The oil is cooling the bearing as well as lubricating, it's centrifugal force that is providing  the pressure, as long as sufficient oil is entering the crank flow through removes heat.   Terry.

[Colin Reed]

HI All,
One thing that is not fully understood is the Crush on shells is to make sure that the back of the shells is making Full contact with the rod I have all ways  Blued the shells and check for crush, the blueing is to make sure there is 100% contact for heat transfer any thing less can be Disaster .
The only Hole I put in rods is 1.5 to 2. mm on the thrust side aimed at the underside of the Piston,
two reasons supply oil for the gudgeon   and cooling for underside of piston.

Just my way of doing things

Colin
NZ

[Zetomagneto]

Zeto you can increase side clearance to improve flow but you need to get some heat into the oil before driving,you get a better flow through by drilling.The oil is cooling the bearing as well as lubricating, it's centrifugal force that is providing  the pressure, as long as sufficient oil is entering the crank flow through removes heat.   Terry.

Terry, I agree that centrifugal force gives pressure to the oil at the point where it is exiting the crankpin hole, however it is hydrodynamic pressure between the two surfaces which prevents metal to metal contact.The oil is heated in the bearing by shearing, and as you say if there is insufficient flow the oil ,and therefore the bearing will overheat.
Your experience shows that drilling the holes appears to have no detrimental effect, but I am not convinced it is necessary.

Colin, I meant to say if your rods are currently undersize, and the white metal is sound no need to remetal, get them bored and narrowed to suit the new crank.prior to dealing with the big ends,Check small ends for wear, as Bob Foreman says there is so little material it makes it difficult, or perhaps inadvisable to bush them

[Ruairidh Dunford]

Austin splash fed shell bearings and rods have holes the same position as those shown in Terry’s photo.

[Stuart Giles]

Unless finished in place all shells are made with an exaggerated clearance at the parting line although it may not be obvious.

Bob, surely you mean interference? (or 'crush' as it's known in the trade). The shells stand a few thou proud of their housing so they are forced firmly into it on assembly. It is this radial force (not the tabs) which prevents the bearing shells turning in service.

I think what Bob is referring to here is the fact that big end bearing shells aren't usually a uniform thickness, they are thinner near the split line, so will present an oval hole giving greater side clearance to the crankpin even though they will (hopefully) be sitting with an element of "crush" in a dead round hole in the big end. You can see this quite clearly  if you use Plastiguage near the split line of a shelled big end and then repeat in the centre of the big end cap

It's certainly true that soft white metal will absorb particles, but the load a white metal bearing will take is a lot less than a thinwall shell bearing of similar area. Also, with a white metalled bearing you are dependent on the quality of the metalling process as well as well as the material used. It's not too clear in this photo of a Ford Model "A" rod from my workshop, but this "run" big end has large areas (the grey bits) where there is no tinning, so, when the white metal got hot, it just melted rather than conducting the heat away through the rod. It probably looked just fine when it came back from the (US based)  metallers. Aftermarket shell bearings are available for Ford Model "A" rods, so problem solved in this case.



I do think that shell Vs. white metal bearings  in vintage motors is to some extent a religious debate; if so, I suppose I have declared my allegiance above .

[Colin Wilks]

I always steer clear of religion and politics, but as far as the white metalling goes I have my rods booked in with Ian Burlngham at Malton, so I think I'm in safe hands.

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Zetomagtneto said "Check small ends for wear, as Bob Foreman says there is so little material it makes it difficult, or perhaps inadvisable to bush them". I think Bob was meaning it was inadvisable to address wear by machining the little ends oversize to fit oversize pins.

I am a bit foxed foxed here. I haven't got the engine out of the car yet so I haven't seen the rods, but being fully floating gudgeon pins I had imagined the little ends would be bushed anyway, and so any wear could be addressed by renewing the bushes, always assuming the rods are otherwise sound?